In recent years, a variety of electronic devices such as light-emitting elements or organic semiconductors in which an organic compound which has photoelectric function as well as reversible oxidation-reduction characteristics and can form amorphous film by itself is used as an organo-electronic material, for example, as a hole transporting agent, have attracted considerable attention. Such an amorphous film of organic compound is formed by preparing a coating composition comprised of a binder resin such as polycarbonate resin and the organic compound dissolved in a suitable organic solvent and then by coating and drying the composition (JP-A-11-174707). In the case of a polynuclear aromatic tertiary amine called a “star-burst” compound, it is vacuum evaporated onto a substrate to directly form a thin film (JP-A-08-291115).
According to a method using a binder resin among the methods mentioned above, the organic compound is diluted with the binder resin in the resulting thin film and influenced by the binder resin so that the organic compound cannot exhibit sufficiently the functions that it originally has as an organo-electronic functional material. In addition, if the organic compound forms a thin film that is stable at normal temperature with the aid of a binder resin, the organic compound has a low glass transition temperature so that the film is poor in heat resistance and has a problem in stability and life.
Under these circumstances, polynuclear aromatic tertiary amine compounds called the “star-burst” molecules are attracting considerable attention as organo-electronic functional materials since they are capable of forming stable thin film by vacuum evaporation. The star-burst molecules are divided into three groups based on their molecular structures: compounds having a triphenylamine structure (triphenylamines), compounds having a triaminobenzene structure (triaminobenzenes) and compounds having a triphenylbenzene structure (triphenylbenzenes).
A variety of “star-burst” molecules inclusive of the triaminobenzenes have been proposed. For example, as such triaminobenzenes, 1,3,5-tris(N-(p-methylphenyl)-N-(1-naphthyl))-amino benzene (p-MTPNAB) and 1,3,5-tris(N-(p-methylphenyl)-N-(4-biphenylyl)amino)benzene (p-MTPBAB) have been proposed (JP-A-2004-155754) These triaminobenzenes are reversible in oxidation-reduction process and have high relatively high glass transition temperatures, i.e., 87° C. and 98° C., respectively. However, there is still a fear that they have not enough stability in performance and durability for use as organo-electronic functional material.
Recently there have been proposed 1,3,5-tris(N-(4′-methyl-4-biphenylyl)-N-(4-methylphenyl)amino)benzene (JP-A-2005-190993) represented by the formula (1)
and 1,3,5-tris(N,N-bis(4′-methyl-4-biphenylyl)amino)benzene (JP-A-2005-276802) represented by the formula (2)

These 1,3,5-tris(diarylamino)benzenes are excellent in stability of repeated oxidation-reduction process compared with the triaminobenzenes which have hitherto been known, and have a higher glass transition temperatures. On the other hand, in these 1,3,5-tris-(diarylamino)benzenes, all the three diarylamino groups have the same chemical structure, that is, all the substituents which the three diaryl amino groups have are the same. Thus, these 1,3,5-tris-(diarylamino)benzenes have symmetry in molecular structure and high crystallinity, and accordingly, they have high melting points. As results, they need high evaporation temperature when they are vacuum evaporated to form thin film. Therefore, there is a problem that these 1,3,5-tris(diarylamino)benzenes thermally decompose when they are vacuum evaporated to form thin film.
The invention has been accomplished to solve the above-mentioned problems involved in the 1,3,5-tris(diarylamino)-benzenes which have heretofore been known. Accordingly, it is an object of the invention to provide a novel 1,3,5-tris(diarylamino)benzene which has characteristics excellent as organic electronic functional material, and which in addition can form thin film by vacuum evaporation at a relatively low temperature. It is a further object of the invention to provide an organic electronic functional material, in particular, a hole injecting and/or transporting agent which comprises such a 1,3,5-tris(diarylamino)benzene.